The prior art reflects quite some examples of conical arrangement of elongated material on a spool.
For example, EP-A1-0 241 964 discloses a way of conical winding metal wire on a spool with a cylindrical core and with at least one conical flange. The winding layers are conically arranged with respect to the cylindrical core. The conical winding layers have the advantage of forming a stable structure with a strongly reduced danger that the windings will slide down the core of the spool, when the spool is positioned vertically.
DE-A1-38 11 284 discloses another way of conical winding wire material. Conical layers are built on a spool with a cylindrical core and with two planar flanges. This embodiment also has the advantage of providing a stable coil.
BE-A3-1 000 634 discloses an improvement whereby the conical coil of wire made by conical layers receives additional conical layers of wire with a reducing number of windings so that the external final form becomes a cylindrical jacket. This embodiment has the advantage of adding weight to the same spool.
A further evolution is disclosed in U.S. Pat. No. 5,255,863. Here strand-like material is wound in conical layers on a conical core of a spool with planar flanges. The angle of the conical core is opposite to the angle of the conical layers. The advantage of this counter-conical winding on a conical core is that after winding, one may take away the flanges and the core, since a stable coreless coil has been left over.
Spools are only temporary storage of the elongated material. Sooner or later, the elongated material has to be unwound from the spool for further or final use. Despite the fact that the prior art embodiments all have the advantage of providing a stable coil, the prior art embodiments have the drawback that unwinding, and particularly stationary unwinding, may cause problems which often lead to fracture of the elongated material. It is hereby understood that the terms ‘stationary unwinding’ refer to a method of unwinding where the spool is not rotated but stands still.